feat: add a production_deploy input to netlify-deploy workflow

[browniebroke]

Why

The netlify-deploy reusable workflow decides between a production and a draft
deploy from github.event_name == 'push' && github.ref_name == 'main'. That
makes it unusable for a production deploy triggered by any other event — the
motivating case being a repository_dispatch sent by a Sanity webhook when new
content is published, to rebuild a statically generated site.

What

Adds an optional production_deploy boolean input, defaulting to the exact
expression used until now, so existing callers keep their current behaviour
(production on a push to main, draft deploy otherwise).

The input drives both the production-deploy option of nwtgck/actions-netlify
and the PRODUCTION_DEPLOY environment variable passed to the build script.

A caller can now force a production deploy:

jobs:
  deploy:
    uses: browniebroke/github-actions/.github/workflows/netlify-deploy.yml@v1
    with:
      netlify_site_id: "..."
      production_deploy: true
    secrets:
      netlify_auth_token: ${{ secrets.NETLIFY_AUTH_TOKEN }}

Note: the github context is allowed in on.workflow_call.inputs.<id>.default,
and is evaluated against the caller's triggering event, which is what makes the
default work.

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